Watermelon have as a rule a rich red flesh that is especially refreshing due 
to the fact that this fruit is 91% water. It is not a muskmelon, like other 
melons but is in fact a member of the gourd family. Grown in tropical 
climates, and in the warmer areas of the United States and Europe, it is 
available most of the summer months and into the early Autumn months as
 well. It comes long and oblong, or short and round depending upon the 
variety. It can have a deep green skin, or one that has green and gold 
stripped variegated skin, or one that has a star and moon shape...quite a 
tasty Heirloom  variety. It can also have a gray/green skin. The fruit, when
 ripe is firm and dark red, and the seeds are dark, but still tender. Avoid 
watermelon that seem light for their size, or watermelon with cracks, soft 
spots or mold. You can purchase cut watermelon, but again beware
 watermelon with soft spots, or fissures in the meat...this means that they
 are over ripe and will be mushy and mealy and tasteless. The sugar has 
converted to starch and the melon will taste terrible. For vine ripened sweet
taste, look for watermelon with the stem end slightly sunken and calloused.

One serving of watermelon (150-gram edible portion, about 5 1/4 ounces) is 
very low in sodium. Watermelon is a good source of Vitamin C. Watermelon
contains no cholesterol of dietary significance and only a small amount of fat
It is an important source of potassium and may micronutrients.

Water-soluble fiber has been determined for the first time in a major nutrition 
survey of the watermelon. Water-soluble comprises 82 percent of the total
dietary fiber in the watermelon. Dietary intake of this class of fiber has been 
shown in clinical studies to reduce serum cholesterol and has been 
associated with many other health benefits. 

Watermelon is a thirst quenching fruit, used in salads, sliced and eaten out 
of hand, or dressed with a light vinaigrette.

Here is a selection of juicy Watermelon sources to link up to:

http://www.watermelons.com/nwa/nutrition.html

http://www.watermelon.org/

http://www.watermelons.com/tex-ok/nutrition.html